This invention relates to a process for the reclamation and rerefining of waste hydrocarbon lubricating oils. In particular, the invention incorporates distillation and solvent extraction in a process for removing impurities from waste oil. The distillation portion of the process reduces coking, cracking and fouling tendencies that are inherent in other distillation rerefining processes while increasing the yield of product.
Each year large and increasing volumes of used lubricating oil, particularly crankcase oils from diesel, gasoline and other internal combustion engines are produced. These waste oils are contaminated with oxidation and degradation products, water, fine particulates including metal, and carbon oil additive products. These contamination components render the oils unsuitable for continued use. Waste oils have generally been disposed by incineration, in land fill, or used in road oiling for dust control, because the cost of reclamation and rerefining has been excessive. However, because of the rising cost of hydrocarbon fuels and lubricants, coupled with the ever-increasing demand and depletion of resources, the need for an efficient, low-cost waste oil rerefining process has arisen.
In recent years, some small scale rerefining processes have been put into operation in which marketable oils are recovered. However, due to the high costs involved and the resulting narrow profit margin, such recovery processes represent a small percentage utilization of the total quantity of used lubricating oils.
The ever-increasing scarcity and consequent rising costs of petroleum, particularly high quality lubricating stocks, now presents positive incentives to selectively remove undesirable contaminants from used motor oils and reuse the valuable high quality lubricating components contained in such oils. Several waste oil rerefining processes are known from the prior art. For example, in U.S. Pat. No. 3,639,229, a process is described where a mixture of an aliphatic monohydric alcohol of from 4 to 5 carbon atoms and a light hydrocarbon is added to waste oil. The mixture settles into three distinct layers. The upper oily layer is recovered, treated with sulfuric acid and thereafter refined by conventional means. In U.S. Pat. No. 3,919,076, a process is described that involves removing water from the waste oil, adding the saturated hydrocarbon solvent, settling the mixture to recover the oil/solvent mix, removing the solvent, vacuum distilling the residual oil to collect selected fractions, hydrogenating the fractions in the presence of a catalyst, stripping hydrogenated oil to remove light ends and filtering the remaining product. U.S. Pat. No. 4,124,492 discloses a process for reclaiming useful hydrocarbon oil from contaminated waste oil in which the waste oil is dehydrated and, thereafter, the dehydrated oil is dissolved in selected amounts of isopropanol. The undissolved waste matter is separated and the residual oil/solvent fraction is distilled to recover the decontaminated oil and solvent. The recovered oil is further clarified by treatment with a bleaching clay or activated carbon at elevated temperatures. In U.S. Pat. No. 4,021,333, a process is described for rerefining used oil that includes distilling of a volatile forecut from the oil, followed by a conventional type of distillation that may occur at reduced pressure. Use of a demister is preferred to minimize carry-over of material into the distillate. The distillation is continued until the desired recovery is obtained followed by extraction of the impurities present in the distillate.
Thus, a need has arisen for an effective process for purifying waste oil that is economical and which provides increased recovery of lubricating oil.